KR20170142381A - Positive Electrode Active Material Particle Comprising Core Having Lithium Cobalt Oxide and Shell Having Cobalt-Phosphate Based Composition and Method of Manufacturing the Same - Google Patents

Abstract

The present invention provides cathode active material particles having a core including lithium cobalt oxide represented by chemical formula 1, Li_aCo_(1-x-y)M_xMe_yO_2-hA_h(1); and a shell coated on a surface of the core and having cobalt-phosphate based composition. In chemical formula 1, M is at least one sort selected from a group composed of Ti, Mg, Al and Zr, Me is at least one sort selected from a group composed of Ba, Ca, Nb, Ta and Mo, A is oxygen substituted halogen, and 0.95 <= a <= 1.05, 0 <= x <= 0.2, 0 <= y <= 0.2, 0 <= x+y <= 0.2, and 0 <= h <= 0.001. The present invention significantly reduces reactivity with an electrolyte, thereby preventing safety problems like a swelling phenomenon caused by gas generation.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positive electrode active material particle comprising a core containing lithium cobalt oxide and a shell containing a cobalt-phosphorus compound, and a method for producing the positive electrode active material particle. the Same}

The present invention relates to a cathode active material particle comprising a core containing a lithium cobalt oxide and a shell containing a cobalt-phosphorus compound and a method for producing the same.

In recent years, the demand for environmentally friendly alternative energy sources has become an indispensable factor for the future, as the increase in the price of energy sources due to depletion of fossil fuels and the interest in environmental pollution are amplified. Various researches on power generation technologies such as nuclear power, solar power, wind power, and tidal power have been continuing, and electric power storage devices for more efficient use of such generated energy have also been attracting much attention.

Particularly, as technology development and demand for mobile devices increase, the demand for batteries as energy sources is rapidly increasing. Recently, the use of secondary batteries as a power source for electric vehicles (EV) and hybrid electric vehicles (HEV) In addition, the use area has been expanded for use as a power auxiliary power source through a grid, and accordingly, a lot of researches on a battery that can meet various demands have been conducted.

Typically, in terms of the shape of a battery, there is a high demand for a prismatic secondary battery and a pouch-type secondary battery which can be applied to products such as mobile phones with a small thickness, and has advantages such as high energy density, discharge voltage, There is a high demand for lithium secondary batteries such as lithium ion batteries and lithium ion polymer batteries.

At present, LiCoO ₂ , ternary system (NMC / NCA), LiMnO ₄ , LiFePO ₄ and the like are used as a cathode material of a lithium secondary battery. Of these, LiCoO ₂ is expensive and has a lower capacity at the same voltage as the ternary system. Therefore, the use of ternary system is increasing to increase the capacity of the secondary battery.

However, in the case of LiCoO ₂ , since the advantages such as a high rolling density are also clearly present, LiCoO ₂ has been widely used up to now, and studies are under way to increase the operating voltage in order to develop a high capacity secondary battery.

In the case of the lithium cobalt oxide, when applying a high voltage for high capacity, more specifically, when applying a high voltage of 4.5 V or more, Li usage of LiCoO ₂ increases and the surface becomes unstable and gas is generated due to a side reaction with the electrolyte, There is a problem that the stability is deteriorated due to occurrence of a ring phenomenon, the possibility of structural instability is increased, and the lifetime characteristic is rapidly deteriorated.

In order to solve this problem, a technique of forming a separate coating layer by coating a metal such as Al, Ti, Mg or Zr on the surface of the LiCoO ₂ may be used. In the case of the coating layer made of the metal, Thereby deteriorating the performance of the secondary battery.

Therefore, there is a high demand for development of cathode active material based on lithium cobalt oxide which can be used stably even at high voltage.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems of the prior art and the technical problems required from the past.

The inventors of the present application have conducted intensive research and various experiments, and have found that, as will be described later, the cathode active material particles contain lithium cobalt oxide; And a shell coated on the surface of the core and containing a cobalt-phosphorus compound, the reactivity with the electrolytic solution is significantly reduced as compared with the conventional cathode active material particle containing only lithium cobalt oxide, It is possible to prevent the deterioration of safety such as swelling due to the swelling phenomenon due to the high operating voltage of the cobalt-phosphorus oxide contained in the shell. Therefore, the structural stability of the cathode active material particles can be improved It is possible to improve the lifetime characteristics of the secondary battery and to easily prevent the deterioration of the rate characteristic of the secondary battery due to the relatively easy movement of lithium ions through the shell. I have come to completion.

In order to accomplish the above object, the present invention provides a cathode active material particle,

A core comprising lithium cobalt oxide represented by the following formula (1); And

A shell coated on the surface of the core and comprising a cobalt-phosphorous compound;

. &Lt; / RTI &gt;

Li _a Co _(1-xy) M _x Me _y O _{2 -he h} (1)

M is at least one member selected from the group consisting of Ti, Mg, Al and Zr, Me is at least one member selected from the group consisting of Ba, Ca, Nb, Ta and Mo, Halogen, 0.95? A? 1.05, 0? X? 0.2, 0? Y? 0.2, 0? X + y? 0.2, 0? H?

When the shell containing the cobalt-phosphorus compound is contained, the reactivity with the electrolytic solution is markedly reduced as compared with the conventional cathode active material particle containing only lithium cobalt oxide, so that the safety such as the swelling phenomenon due to gas generation Can be prevented and the surface structure change can be suppressed under a high voltage owing to the high operating voltage of the cobalt-phosphorus oxide contained in the shell. Therefore, the structural stability of the cathode active material particles can be improved, And the movement of lithium ions through the shell is relatively easy, so that it is possible to effectively prevent deterioration of the rate characteristic of the secondary battery.

In one specific example, the weight of the shell relative to the weight of the core may range from 0.5 wt% to 3 wt%.

If the weight of the shell is less than 0.5 wt.%, The ratio of the shell to the cathode active material particles is too small, and the desired effect may not be sufficiently exhibited. On the other hand, The proportion of the shell in the cathode active material particles becomes excessively high and the total capacity of the cathode active material may be relatively decreased.

The cobalt-phosphorous compound of the shell may be coated on the surface of the core in a particle state, or the cobalt-phosphorous compound of the shell may be coated on the surface of the core in a layered structure.

Specifically, the coating structure of the cobalt-phosphorous compound may be caused by a difference in the production method of the cathode active material particles.

More specifically, the cathode active material particles can be produced by a dry method or a wet method, and when the cathode active material particles are manufactured by a dry method, the cobalt-phosphorous compound of the shell is mixed with the lithium cobalt oxide particles constituting the core, The cobalt-phosphorus compound of the shell can be coated on the surface of the core in a layered structure in a completely dissolved state, when the cobalt-phosphorous compound of the shell can be coated on the surface of the core.

On the other hand, the shell may have a structure in which the shell is coated in an area of 50% to 99% with respect to the surface area of the core.

If the shell is coated in an area of less than 50% out of the above range with respect to the surface area of the core, the coating area of the shell is too small and the desired effect may not be sufficiently exhibited. On the contrary, When the shell is coated in an area exceeding 99% with respect to the surface area of the core, migration of lithium ions from the core is suppressed, and the rate characteristic of the secondary battery may be rather deteriorated.

In one specific example, the cobalt-phosphorous compound may be a cobalt-containing phosphate represented by the following formula (2) wherein the oxidation number of cobalt is +2 to +3:

Li _b CoPO ₄ (2)

In the above formula, 0? B?

That is, since the cobalt-phosphorous compound has an oxidation number of cobalt of +2 to +3, the reactivity with the electrolytic solution remarkably decreases even at a high voltage of 4.5 V or more as compared with the conventional cathode active material particles containing only lithium cobalt oxide, It is possible to effectively prevent the generation of gas due to side reactions with the electrolytic solution and the decrease of safety such as swelling phenomenon.

In addition, the core and the shell each contain a lithium element, and the concentration of lithium may exhibit a concentration gradient continuously or discontinuously increasing from the shell toward the center of the core.

That is, the shell may have a structure in which the molar fraction of lithium is 1 or less and the concentration of lithium is relatively low as compared with the core, and accordingly, the lithium may contain a portion lacking lithium.

Therefore, the portion of the shell where the lithium is partially broken can serve as a passage for moving lithium ions from the lithium cobalt oxide of the core. Therefore, the conventional anode including the metal coating layer such as Al, Ti, Mg, It is possible to effectively prevent deterioration in rate characteristics of the secondary battery as compared with the active material particles.

However, the type of the cobalt-phosphorous compound is not limited thereto as long as it can maintain a stable coating state on the surface of the core containing lithium cobalt oxide and exhibit a desired effect. In another specific example , And the cobalt-phosphorous compound may be Co ₃ (PO ₄ ) _{2 in} which the oxidation number of cobalt is +2.

Further, the present invention provides a method for producing the above-mentioned cathode active material particles,

(a) preparing a lithium cobalt oxide and a cobalt-phosphorous compound in a particle state;

(b) dry mixing the lithium cobalt oxide and the cobalt-phosphorous compound; And

(c) heat-treating the dry mixture after the step (b);

. &Lt; / RTI &gt;

That is, the cathode active material particles are produced by a method including dry-mixing lithium cobalt oxide and a cobalt-phosphorous compound in a particle state and heat-treating the lithium cobalt oxide to form a shell containing a cobalt-phosphorus compound on the surface of the core containing lithium cobalt oxide .

Therefore, the cathode active material particles can be more easily manufactured by a relatively simplified method, thereby saving the cost and time required for manufacturing the cathode active material particles, Or the composition of the shell can be easily controlled and the reliability of the manufacturing method can be improved by preventing the defective product which may be caused by the complicated process.

At this time, the cobalt-phosphorous compound may be LiCoPO ₄ .

More specifically, the LiCoPO ₄ is because the oxidation number of cobalt kept below +3, by remarkably reducing the reactivity with the electrolytic solution under high voltage 4.5V or more, it can prevent the problem of deterioration of stability and swelling caused by gas generation have.

In addition, the LiCoPO ₄ has an operating voltage of about 4.9 V, and because of the high operating voltage, the change of the surface structure of the lithium cobalt oxide of the core can be suppressed under a high voltage, thereby improving the structural stability of the cathode active material particle , The lifetime characteristics of the secondary battery can be improved.

Meanwhile, the particle size of the lithium cobalt oxide particles may be 1 micrometer to 20 micrometers, and the particle size of the cobalt-phosphorus compound particles may be 10 to 500 nanometers.

In other words, in the dry production method, the lithium cobalt oxide particles have a relatively large particle size as compared with the cobalt-phosphorous compound particles, and thus the lithium cobalt oxide particles having a relatively large particle size are dispersed in the cathode active material particles And the cobalt-phosphorous compound particles having a relatively small particle size are coated on the surface of the core to form a shell, whereby the cathode active material particles having a more stable core-shell structure .

If the particle size of the lithium cobalt oxide particles or the cobalt-phosphorus compound particles is too small or too large beyond the above range, the core-shell structure of the cathode active material particles can not be stably formed, Can occur.

In addition, the heat treatment in the process (c) may be performed at a temperature in the range of 300 to 900 degrees Celsius, more specifically, in the range of 500 to 700 degrees Celsius for 5 to 20 hours.

If the heat treatment in the step (c) is carried out at an excessively low temperature beyond the above range, or if the heat treatment is carried out for an excessively short time, the core-shell structure of the cathode active material particles may not be stably formed, , The physical and chemical properties of the lithium cobalt oxide and the cobalt-phosphorus compound constituting the cathode active material particles are measured when the heat treatment in the step (c) is carried out at an excessively high temperature beyond the above range or for an excessively long time It may cause performance deterioration.

Further, the cobalt-phosphorous compound may be coated on the surface of the lithium cobalt oxide particles in a particle state after the heat treatment in the step (c).

That is, the cobalt-phosphorous compound can be coated on the surface of the lithium-cobalt oxide particles forming the core while maintaining the particle state through the dry production method, thereby forming a stable core-shell structure.

In another specific example, the present invention provides a method for producing the above-described cathode active material particles, which method comprises:

(i) mixing and dispersing a lithium cobalt oxide precursor in a particle state in a mixed solution of CoCl ₂ .6H ₂ O and H ₃ PO ₄ ;

(ii) dropping (NH ₄ ) ₂ HPO ₄ solution into the solution to cause a coprecipitation reaction; And

(iii) introducing and mixing a lithium source into the solution, followed by heat treatment;

. &Lt; / RTI &gt;

That is, the positive electrode active material particles are prepared by a wet process, wherein the particles forming the core and the shell are mixed in the state of being dissolved in the respective precursor stages to form a basic core-shell structure, and the lithium source is mixed and heat- And the source penetrates into the core, whereby the concentration of lithium can be made to have a predetermined concentration gradient.

Thus, the cobalt-phosphorous compound forming the shell can be coated on the surface of the core in a layered structure by being coated on the surface of the lithium cobalt oxide precursor particles forming the core in the precursor step, Can be formed more uniformly on the surface of the core.

At this time, if the lithium cobalt oxide precursor is capable of stably forming the core-shell structure of the cathode active material particles, the kind thereof is not particularly limited, and may be specifically Co ₃ O ₄ .

Further, a layered shell including (NH ₄ ) CoPO ₄ .zH ₂ O (here, a natural number of 0? Z? ₆ ) is formed on the surface of the lithium cobalt oxide precursor by the coprecipitation reaction of the above process (ii) .

That is, since the cobalt-phosphorous compound forming the shell is coated on the surface of the lithium cobalt oxide precursor forming the core by the wet preparation method, a more uniform layered structure can be formed.

On the other hand, the lithium element provided in the lithium source in the step (iii) may at least form a chemical bond with the lithium cobalt precursor.

In other words, the lithium element provided in the lithium source in the step (iii) penetrates into the inside and forms a chemical bond with the core, thereby forming a lithium cobalt oxide. In this process, Since the chemical bond is preferentially formed, the concentration of lithium can exhibit a concentration gradient that increases continuously or discontinuously toward the center of the core from the shell.

Therefore, the shell of the cathode active material particles may have a structure in which lithium is relatively low in concentration compared to the core, and accordingly, the lithium ion is included in the lithium cobalt oxide at the time of charge / The deterioration of the rate characteristics of the secondary battery can be effectively prevented as compared with the conventional cathode active material particles containing a metal coating layer such as Al, Ti, Mg and Zr.

In one specific example, the heat treatment in process (iii) may be performed in the range of 300 to 1100 degrees Celsius, more specifically in the range of 800 to 1050 degrees Celsius for 5 to 20 hours.

If the heat treatment in the step (iii) is carried out at an excessively low temperature beyond the above range, or if the heat treatment is performed for an excessively short time, the core-shell structure of the cathode active material particles may not be stably formed, , The physical and chemical properties of the lithium cobalt oxide and the cobalt-phosphorus compound constituting the cathode active material particles are measured when the heat treatment in the step (iii) is carried out at an excessively high temperature beyond the above range or for an excessively long time It may cause performance deterioration.

In addition, the present invention provides a secondary battery comprising the positive electrode active material particles, the negative electrode and the electrolyte solution, and the kind of the secondary battery is not particularly limited, but specific examples include a high energy density, A secondary battery such as a lithium ion battery, a lithium ion polymer battery or the like, which has merits such as power, voltage, and output stability.

Generally, a lithium secondary battery is composed of a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte containing a lithium salt.

The positive electrode is prepared, for example, by coating a mixture of a positive electrode active material, a conductive material and a binder on a positive electrode current collector, and then drying the mixture. Optionally, a filler may be further added to the mixture.

The conductive material is usually added in an amount of 1 to 30% by weight based on the total weight of the mixture including the cathode active material. Such a conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, for example, graphite such as natural graphite or artificial graphite; Carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The binder is a component which assists in bonding of the active material and the conductive material and bonding to the current collector, and is usually added in an amount of 1 to 30% by weight based on the total weight of the mixture containing the cathode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene , Polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, various copolymers and the like.

The filler is optionally used as a component for suppressing the expansion of the anode, and is not particularly limited as long as it is a fibrous material without causing a chemical change in the battery. Examples of the filler include olefin polymers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

The negative electrode is manufactured by applying and drying a negative electrode active material on a negative electrode collector, and if necessary, the above-described components may be selectively included.

Examples of the negative electrode active material include carbon such as non-graphitized carbon and graphite carbon; _{Li x Fe 2 O 3 (0≤x≤1} ), Li x WO 2 (0≤x≤1), Sn x Me 1-x Me 'y O z (Me: Mn, Fe, Pb, Ge; Me' : Metal complex oxides such as Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, Halogen, 0 < x &lt; Lithium metal; Lithium alloy; Silicon-based alloys; Tin alloy; _{SnO, SnO 2, PbO, PbO} 2, Pb 2 O 3, Pb 3 O 4, Sb 2 O 3, Sb 2 O 4, Sb 2 O 5, GeO, GeO 2, Bi 2 O 3, Bi 2 O 4, and Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials and the like can be used.

The separation membrane and the separation film are interposed between the anode and the cathode, and an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally 0.01 to 10 mu m and the thickness is generally 5 to 300 mu m. Such separation membranes include, for example, olefinic polymers such as polypropylene, which are chemically resistant and hydrophobic; A sheet or nonwoven fabric made of glass fiber, polyethylene or the like is used. When a solid electrolyte such as a polymer is used as an electrolyte, the solid electrolyte may also serve as a separation membrane.

Further, in one specific example, in order to improve the safety of a high energy density cell, the separation membrane and / or the separation film may be an organic / inorganic composite porous SRS (Safety-Reinforcing Separators) separator.

The SRS separator is manufactured by using inorganic particles and a binder polymer on the polyolefin-based separator substrate as an active layer component. In addition to the pore structure contained in the separator substrate itself, the SRS separator is formed by interstitial volume between inorganic particles And has a uniform pore structure.

The use of such an organic / inorganic composite porous separator has the advantage of suppressing an increase in thickness of the cell due to swelling at the time of chemical conversion compared with the case of using a conventional separator, When a gelable polymer is used when liquid electrolyte is impregnated, it can also be used as an electrolyte.

In addition, the organic / inorganic composite porous separator can exhibit excellent adhesion characteristics by controlling the contents of the inorganic particles and the binder polymer in the separator, so that the cell assembly process can be easily performed.

The inorganic particles are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles usable in the present invention are not particularly limited as long as the oxidation and / or reduction reaction does not occur in the operating voltage range of the applied battery (for example, 0 to 5 V based on Li / Li +). Particularly, when inorganic particles having an ion-transporting ability are used, the ion conductivity in the electrochemical device can be increased and the performance can be improved. Therefore, it is preferable that the ionic conductivity is as high as possible. In addition, when the inorganic particles have a high density, it is difficult to disperse the particles at the time of coating, and there is a problem of an increase in weight during the production of the battery. In the case of an inorganic substance having a high dielectric constant, dissociation of an electrolyte salt, for example, a lithium salt, in the liquid electrolyte also contributes to increase ionic conductivity of the electrolyte.

The nonaqueous electrolyte solution containing a lithium salt is composed of a polar organic electrolyte and a lithium salt. As the electrolytic solution, a non-aqueous liquid electrolytic solution, an organic solid electrolyte, an inorganic solid electrolyte and the like are used.

Examples of the nonaqueous liquid electrolytic solution include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma -Butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane , Acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate Nonionic organic solvents such as tetrahydrofuran derivatives, ethers, methyl pyrophosphate, ethyl propionate and the like can be used.

Examples of the organic solid electrolyte include a polymer electrolyte such as a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, an agitation lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride, Polymers containing ionic dissociation groups, and the like can be used.

Examples of the inorganic solid electrolyte include Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Nitrides, halides and sulfates of Li such as Li ₄ SiO ₄ -LiI-LiOH and Li ₃ PO ₄ -Li ₂ S-SiS ₂ can be used.

The lithium salt is a material that is readily soluble in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO 4, LiBF 4, LiB 10 Cl 10, LiPF 6, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF _{6, LiSbF 6, LiAlCl 4,} CH 3 SO 3 Li, CF 3 SO 3 Li, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate and imide have.

For the purpose of improving the charge-discharge characteristics and the flame retardancy, the non-aqueous liquid electrolyte may contain, for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, N, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, aluminum trichloride, etc. are added It is possible. In some cases, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride may be further added to impart nonflammability, or a carbon dioxide gas may be further added to improve high-temperature storage characteristics.

The present invention also provides a battery pack including the secondary battery and a device including the battery pack. Since the battery pack and the device are known in the art, a detailed description thereof will be omitted herein. do.

As described above, the cathode active material particle according to the present invention comprises a core containing lithium cobalt oxide; And a shell coated on the surface of the core and containing a cobalt-phosphorus compound, the reactivity with the electrolytic solution is significantly reduced as compared with the conventional cathode active material particle containing only lithium cobalt oxide, It is possible to prevent the deterioration of safety such as swelling due to the swelling phenomenon due to the high operating voltage of the cobalt-phosphorus oxide contained in the shell. Therefore, the structural stability of the cathode active material particles can be improved The lifetime characteristics of the secondary battery can be improved, and the movement of lithium ions through the shell is relatively easy, so that it is possible to effectively prevent the deterioration of the rate characteristic of the secondary battery.

1 is a graph showing a maximum current arrival time according to Experimental Example 1 of the present invention;
2 is a graph showing the capacity retention rate measured according to Experimental Example 2 of the present invention.

Hereinafter, the present invention will be further described with reference to Examples of the present invention, but the scope of the present invention is not limited thereto.

Cathode active material manufacturing

&Lt; Example 1 >

LiCoO ₂ in a particle state having a particle diameter in the range of 10 to 20 micrometers and LiCoPO ₄ in a particle state having a particle diameter in a range of 100 to 300 nm were prepared. 100 parts by weight of LiCoO ₂ , 1.30 parts by weight of PVdF and 1 part by weight of LiCoPO _{4 were} dry mixed and then heat-treated at 700 ° C. for 10 hours to obtain a shell containing LiCoO ₂ on the core, LiCoPO ₄ was prepared.

&Lt; Example 2 >

As a precursor of LiCoO ₂ , Co ₃ O ₄ in a particle state in which the particle diameter is distributed in a range of 10 to 20 micrometers was prepared. 50 g of Co ₃ O ₄ in the above particle state was mixed and dispersed in 500 ml of a solution in which CoCl ₂ .6H ₂ O and DI water were mixed at a weight ratio of 1:30, and then (NH ₄ ) ₂ HPO ₄ and DI water 1: 20 by weight drop by drop to cause a coprecipitation reaction to form a layered shell having (NH ₄ ) CoPO ₄ .H ₂ O on the surface of Co ₃ O ₄ . After the completion of the coprecipitation reaction, 23.24 g of Li ₂ CO ₃ was added and mixed as a lithium source, and the mixture was heat-treated at 1000 ° C. for 10 hours. The weight ratio of core to shell was 99: 1, Of the cathode active material layer continuously increases with the center of the core, and the lithium element chemically bonds with at least Co ₃ O _{4 of the} core to form lithium cobalt oxide.

&Lt; Example 3 >

The same cathode active material particles as in Example 2 were prepared except that the weight ratio of core to shell was adjusted to be core: shell = 95: 5.

<Example 4>

The same cathode active material particles as in Example 2 were prepared, except that the weight ratio of core to shell was set to be core: shell = 90: 10.

&Lt; Comparative Example 1 &

Instead of LiCoPO ₄ , Al was used to produce the same cathode active material particles as in Example 1, except that the shell coated on the surface of the core contained Al.

Secondary battery manufacturing

The cathode active material particles, the PVdF binder, and the natural graphite conductive material prepared in Examples 1 to 4 and Comparative Example 1 were thoroughly mixed with NMP so as to have a weight ratio of 95: 2.5: 2.5 (cathode active material: binder: conductive material) Thick Al foil, and dried at 130 DEG C to prepare a positive electrode. Lithium foil was used as the cathode, and an electrolyte solution containing 1 M of LiPF ₆ in a solvent of EC: DMC: DEC = 1: 2: 1 was used to prepare a half coin cell.

Electrolyte reactivity

<Experimental Example 1>

The half-cell including the cathode active material particles of Examples 1 and 2 and Comparative Example 1 was continuously charged in a CC / CV mode at an upper limit voltage of 4.55 V at 60 degrees Celsius to measure a time to reach a maximum current The results are shown in Table 1 and Fig.

Comparative Example 1 Example 1 Example 2 Maximum current arrival time (h) 80 134 158

Referring to Table 1, in the case of Examples 1 and 2, the surface of the lithium cobalt oxide core was coated with a shell containing a cobalt-phosphorus compound, so that the reactivity with the electrolytic solution was remarkably reduced even at a high voltage of 4.5 V or more , It can be seen that the maximum current reaching time is relatively longer than that of Comparative Example 1. [ On the other hand, in the case of Comparative Example 1, although Al was coated on the surface of the lithium cobalt oxide, the reaction with the electrolytic solution was actively performed at a high voltage of 4.5 V or more, and the maximum current reaching time was relatively short .

Life characteristics

<Experimental Example 2>

The half-cell including the cathode active material particles of Examples 1 and 2 and Comparative Example 1 was charged and discharged for 50 cycles in a CC / CV mode at an upper limit voltage of 4.55 V at a room temperature of 25 degrees Celsius, And the results are shown in Table 2 and Fig. 2 below.

Comparative Example 1 Example 1 Example 2 Capacity retention rate (%) 74 86 91

Referring to Table 1, in the case of Examples 1 and 2, the surface of the lithium cobalt oxide core was coated with a shell containing a cobalt-phosphorus compound, so that stability of the surface was improved even at a high voltage of 4.5 V or higher, , And the capacity retention rate is 86% or more. On the other hand, in the case of Comparative Example 1, although the surface of the lithium cobalt oxide was coated with Al, the surface was unstable under a high voltage of 4.5 V or more, and the capacity retention rate was 74% have.

Capacity characteristics

<Experimental Example 3>

The half-cell including the cathode active material particles of Example 2 and Examples 3 and 4 was charged and discharged for 50 cycles in a CC / CV mode at an upper limit voltage of 4.55 V at a room temperature of 25 degrees Celsius, And the results are shown in Table 3 below.

Example 2 Example 3 Example 4 Capacity retention rate (%) 91 90 85 Initial charge capacity (mAh / g) 215 206 215

Referring to Table 3, it can be seen that the capacity retention ratio and initial charge capacity are the best in the case of Example 2 in which the weight of the shell in the cathode active material particle is 1 wt% based on the weight of the core. In the case of Example 3 in which the weight of the shell is 5 wt% relative to the weight of the core, since the surface protective effect of the shell is the same, the capacity retention ratio is kept substantially equal but the cobalt-phosphorus compound which is electrochemically inactive in the usable voltage range is included , The initial charge capacity is decreased. In addition, in the case of Example 4 in which the weight of the shell was 10% by weight relative to the weight of the core, both the capacity retention ratio and the initial charge capacity were confirmed to be lower than those in Example 2. Therefore, in the cathode active material particle, the core and the shell may exhibit a more optimal effect when they constitute a specific weight ratio. Specifically, in the cathode active material particle, the weight of the shell is 0.5 wt% to 3 wt% Is most preferable.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims (21)

A core comprising lithium cobalt oxide represented by the following formula (1); And
A shell coated on the surface of the core and comprising a cobalt-phosphorous compound;
The positive electrode active material particles according to claim 1,
Li _a Co _(1-xy) M _x Me _y O _{2 -he h} (1)
M is at least one member selected from the group consisting of Ti, Mg, Al and Zr, Me is at least one member selected from the group consisting of Ba, Ca, Nb, Ta and Mo, Halogen, 0.95? A? 1.05, 0? X? 0.2, 0? Y? 0.2, 0? X + y? 0.2, 0? H? The positive electrode active material particle according to claim 1, wherein the weight of the shell relative to the weight of the core is 0.5 wt% to 3 wt%. The cathode active material particle according to claim 1, wherein the cobalt-phosphorous compound of the shell is coated on the surface of the core in a particle state. The cathode active material particle according to claim 1, wherein the cobalt-phosphorous compound of the shell is coated on the surface of the core in a layered structure. The positive electrode active material particle according to claim 1, wherein the shell is coated in an area of 50% to 99% with respect to the surface area of the core. The positive electrode active material particle according to claim 1, wherein the cobalt-phosphorous compound is a cobalt-containing phosphate represented by the following formula (2) wherein the oxidation number of cobalt is +2 to +3:
Li _b CoPO ₄ (2)
In the above formula, 0? B? The positive electrode active material particle according to claim 1, wherein the core and the shell each contain a lithium element, and the concentration of lithium exhibits a concentration gradient continuously or discontinuously increasing from the shell toward the center of the core. The positive electrode active material particle according to claim 1, wherein the cobalt-phosphorous compound is Co ₃ (PO ₄ ) ₂ having an oxidation number of cobalt of +2. A method for producing a cathode active material particle according to claim 1,
(a) preparing a lithium cobalt oxide and a cobalt-phosphorous compound in a particle state;
(b) dry mixing the lithium cobalt oxide and the cobalt-phosphorous compound; And
(c) heat-treating the dry mixture after the step (b);
Wherein the positive electrode active material particles have an average particle diameter of not more than 100 nm. The method according to claim 9, wherein the cobalt-phosphorous compound is LiCoPO ₄ . The method according to claim 9, wherein the particle size of the lithium cobalt oxide particles is 1 micrometer to 20 micrometers, and the particle size of the cobalt-phosphorus compound particles is 10 to 500 nanometers. The method according to claim 9, wherein the heat treatment in step (c) is performed at a temperature in the range of 300 to 900 degrees Celsius for 5 to 20 hours. The method of claim 9, wherein the cobalt-phosphorous compound is coated on the surface of the lithium cobalt oxide particle in a particle state after the heat treatment in the step (c). A method for producing a cathode active material particle according to claim 1,
(i) mixing and dispersing a lithium cobalt oxide precursor in a particle state in a mixed solution of CoCl ₂ .6H ₂ O and H ₃ PO ₄ ;
(ii) adding a solution containing (NH ₄ ) ₂ HPO ₄ to the solution to cause a coprecipitation reaction; And
(iii) introducing and mixing a lithium source into the solution, followed by heat treatment;
Wherein the positive electrode active material particles have an average particle diameter of not more than 100 nm. 15. The method of claim 14, wherein the lithium cobalt oxide precursor is Co ₃ O ₄ . 15. The method according to claim 14, wherein the surface of the lithium cobalt oxide precursor is coated with a layered structure including (NH ₄ ) CoPO ₄ .zH ₂ O (where 0? Z? ₆ ) And a shell is formed on the surface of the cathode active material particle. 15. The method according to claim 14, wherein the lithium element provided in the lithium source of the step (iii) forms at least a chemical bond with the lithium cobalt precursor. 15. The method according to claim 14, wherein the heat treatment in step (iii) is performed at a temperature in the range of 300 to 1100 degrees Celsius for 5 to 20 hours. A secondary battery comprising a cathode, a cathode, and an electrolyte containing the cathode active material particles according to claim 1. A battery pack comprising a secondary battery according to claim 19. A device comprising a battery pack according to claim 20.

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